1. Field of the Invention
The invention relates generally to the device configuration and manufacturing methods for fabricating the semiconductor power devices. More particularly, this invention relates to an improved device configuration for providing the MOSFET device with embedded junction barrier Schottky diode above split body regions to improve operation efficiency with reduced areas occupied by the Schottky diodes while reducing reverse current because of current pinch-off of the adjacent body regions.
2. Description of the Related Art
In order to increase the efficiency of a semiconductor power device, a Schottky diode is often implemented as a clamping diode in parallel to the parasitic PN body diode to prevent the body diode from turning on. Once the parasitic PN body diode is turned on, both electron and hole carriers are generated that requires longer time to eliminate these carriers through the electron-hole combinations. The Schottky diode is implemented to prevent the turning-on of the parasitic PN diode and furthermore, the Schottky diode is operated with a single carrier, e.g., the carriers consisted of electrons only, and these single type of carriers can be drawn from the drain electrode. Therefore, Schottky diode is an effective and preferred clamping diode to increase the operational efficiency of the semiconductor power device. The Schottky clamping operation can be realized when the forward Vf voltage of the Schottky diode is less than the parasitic diode that is approximately 0.7 volts. Furthermore, the Schottky diode must have a low reverse current that is generally lower than ten milli-amperes (mA).
A typical application of the Schottky diode in a semiconductor power device is shown in FIG. 1A that illustrates the application of a semiconductor power device, e.g., a MOSFET is a high efficiency DC/DC converter. A Schottky diode is externally added in parallel with the MOSFET device to prevent the parasitic PN diode of the MOSFET from inadvertently turn on thus increase the operational efficiency of the DC/DC converter. However, the implementation of an external Schottky diode increases the size of the DC/DC converter and also requires additional manufacturing processes to connect the external Schottky to the MOSFET. An integration of the Schottky diode with the semiconductor power device as a single integrated circuit (IC) chip is certainly more desirable for simplifying the manufacturing processes and to reduce the size and costs of the semiconductor power device.
In U.S. Pat. No. 6,351,018, Sapp discloses a trench MOSFET implemented with trench Schottky diodes as shown in FIG. 1B. The trench Schottky diodes as disclosed by Sapp however occupy additional space that is approximately the same size as the MOSFET device itself. Furthermore, the trench Schottky diode suffers an disadvantage the there is a high leakage current between the drain and the source due to the increase of the phosphorous dopant concentration at the channel regions with the dopant ions diffuse to the channel regions during the sacrificial and gate oxidation processes. The Schottky diodes as disclosed further have higher capacitance due to the present of the MOS structure.
Kinzer discloses another semiconductor power device in U.S. Pat. No. 6,433,396 implemented with planar Schottky diodes as shown in FIG. 1C. The planar Schottky diodes are formed in a separate planar Schottky diode area. Again, the configuration requires a larger area due to the additional space occupied by the planar Schottky diodes. Furthermore, one additional contact mask is required to form the planar Schottky diodes in the specially assigned area for the planar Schottky diodes. The production cost is increased due to the additional mask requirement. Moreover, the leakage current of the embedded planar Schottky diodes are much higher than the trench Schottky diodes and conventional Junction barrier diodes.
In U.S. Pat. No. 6,998,678, Werner et al. disclose anther semiconductor power device implemented with trench Schottky diodes as shown in FIG. 1D. The trench Schottky diodes are formed adjacent to and in parallel to the trench gates in the semiconductor substrate. Each Schottky diode is connected in parallel with a drain-source path (D-S) and is formed by a Schottky contact between a source electrode and the semiconductor body near the bottom of the trenches parallel to the trench gates. The device disclosed by Werner still suffers the disadvantage that additional spaces are occupied by the trench Schottky diodes and furthermore, additional P+ mask is required to form the Schottky diodes.
Therefore, a need still exists in the art of power semiconductor device design and manufacture to provide new manufacturing method and device configuration in forming the semiconductor power devices such that the above discussed problems and limitations can be resolved.